If $a + b = 1$ and $x + y + z = 9$, what is $4y + 6b + 6a + 4z + 4x$ ?
Solution: $= 6a + 6b + 4x + 4y + 4z$ $= (6) \cdot (a + b) + (4) \cdot (x + y + z)$ $= (6) \cdot (1) + (4) \cdot (9)$ $= 6 + 36$ $= 42$